Process for producing sandwich structure and adhesive film therefor

ABSTRACT

A process for producing a sandwich structure, includes laminating a reinforced fiber material which is substantially free from a matrix resin; a glycol modified copolymerized polyester resin film; a thermosetting resin composition film which is hardened at room temperature; a core material selected from an open cell foam and a honeycomb; a thermosetting resin composition film which is hardened at room temperature; a glycol modified copolymerized polyester resin film; and a reinforced fiber material which is substantially free from a matrix resin, in this order in a molding tool to form a sandwich, hardening the thermosetting resin composition film which is hardened at room temperature under a condition that the molding tool is closed, infusing a matrix resin into the molding tool, and adjusting a temperature in the molding tool at room temperature or a hardening temperature of the matrix resin to harden the matrix resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for infusing and molding aliquid resin for producing a sandwich structure in a block, withoutperforming pretreatment on a core material.

2. Description of Related Art

Currently, fiber reinforced resin compositions are widely used becausethey are light in weight and very strong. In particular, a filamentreinforced thermosetting resin composition has been advantageously usedin airplanes, ships, railroad vehicles, cars, golf clubs, tennisrackets, etc., as a substitute for a metal material because it is lightin weight, has high rigidity, and is very strong. In addition, furtherreduction in weight can be anticipated because of the dynamicscharacteristic thereof, and hence a sandwich structure material isattractive.

However, in general, the sandwich structure material is produced bylaminating a prepreg, then heating the resultant laminated prepreg in anautoclave under a pressurized condition, and hence the conventionalmethod has a problem in that it necessitates a large amount of labor,thermal energy, and plant-and-equipment investment, thereby makingmanufacturing and processing cost high. Then, a method of pouring aliquid thermosetting resin into glass or carbon fiber textiles and thenhardening it has been developed, which is called RTM (Resin TransferMolding) and VARTM (Vacuum-Assisted RTM). In this method, an expensiveprepreg is not used, the textiles are laminated simply, and an autoclaveis not used, and hence production of a fiber reinforced resincomposition can be performed at a cost lower than that of the prepregmethod.

However, the above method of pouring the liquid resin, such as RTM andVARTM, is not suitable for producing the sandwich structure materialusing hollow cores of which the surfaces are not closed, such as ahoneycomb core and an open cell foam core, because the liquid resinenters into the hollow cores to increase the core weight remarkably.Therefore, it is necessary to adhere the facing material to the corematerial which were fabricated separately according to the conventionalmethod, to obtain a sandwich structure material. Recently, a methodwhich includes heating and adhering a cover material to a core materialbeforehand to obtain a fabricated core material, installing thefabricated core material as well as the other members in a mold,clamping or bagging the mold, and thereafter pouring a liquid resin intothe mold to mold has also been developed. However, this method requiresa step for fabricating the core as an individual step, and moreover,this method has a problem in that when the molded object has a curvedsurface, it requires a metal mold for fabricating the core material toform the curved surface of the core material, in addition to the mainmold for preparing the sandwich structure material, thereby increasingproduction cost.

In the Japanese Unexamined Patent Application, First Publication No.2003-39579, the use of impermeable resin film and the non-low viscositytype film is disclosed, and in the Japanese Unexamined PatentApplication, First Publication No H09-295362, the use of a specificresin and/or moisture cover film, and a film adhesive is disclosed.Moreover, in the Japanese Unexamined Patent Application, FirstPublication No. 2000-167950, application of a seal material which hasthermosetting type adhesive performance is disclosed. However, althoughthe producing process of these sandwich structures can be performed inbatch processing in a metal mold, since it is necessary to heat itbefore pouring liquid resin therein, it is necessary to harden theadhesives and the seal material to seal the honeycomb core etc., andhence there is still a problem of the heating and hardening processbeing necessary to seal the core.

Thus, in the conventional method, heating is necessary to seal thehollow core of which the surface has not been closed, such as ahoneycomb core and an open cell foam core. Particularly, in VARTMfabrication of a large article, a large oven is necessary, and theequipment expense and operating cost increase. Therefore, a method whichcan eliminate the heating process, and reduce consumption energy andlabors is desired strongly.

Therefore, it is an object of the present invention to provide a processfor producing a sandwich structure and an adhesive film used therefor,which can overcome the problem of the conventional technique. Morespecifically, it is an object of the present invention to provide aprocess for producing a sandwich structure and an adhesive film usedtherefor, which can produce a sandwich structure at a low cost, lowenergy consumption, and low labor, without heating and large scaleequipment.

SUMMARY OF THE INVENTION

The process for producing a sandwich structure of the present inventionincludes: laminating a reinforced fiber material which is substantiallyfree from a matrix resin; a glycol modified copolymerized polyesterresin film; a thermosetting resin composition film which is hardened atroom temperature; a core material selected from an open cell foam and ahoneycomb; a thermosetting resin composition film which is hardened atroom temperature; a glycol modified copolymerized polyester resin film;and a reinforced fiber material which is substantially free from amatrix resin, in this order in a molding tool to form a sandwich,hardening the thermosetting resin composition film which is hardened atroom temperature under condition that the molding tool is closed,infusing a matrix resin into the molding tool, and adjusting atemperature in the molding tool at room temperature or a hardeningtemperature of the matrix resin to harden the matrix resin.

Here, a cycloalkanediol modified copolymerized polyester resin may beexemplified as the glycol modified copolymerized polyester resin.

Similarly, a cycloalkanediol modified copolymerized polyethyleneterephthalate resin may be exemplified as the glycol modifiedcopolymerized polyester resin.

Similarly, the glycol modified copolymerized polyester resin film andthe thermosetting resin composition film which is hardened at roomtemperature may previously form an adhesive film consisting of theglycol modified copolymerized polyester resin film and a thermosettingresin composition which is hardened at room temperature, which is helduniformly thereon.

Similarly, the thermosetting resin composition film which is hardened atroom temperature may have a cloth as a carrier.

Similarly, the cloth used as the carrier may be a nonwoven fabric.

Similarly, the thermosetting resin composition which forms thethermosetting resin composition film which is hardened at roomtemperature preferably has a viscosity of 2 to 200 Pa·S.

Similarly, a thermosetting resin composition consisting of a vinylpolymerizable compound may be exemplified as the thermosetting resincomposition which forms the thermosetting resin composition film whichis hardened at room temperature.

Similarly, a vinyl ester resin may be exemplified as the vinylpolymerizable compound.

Similarly, the thermosetting resin composition which forms thethermosetting resin composition film which is hardened at roomtemperature may contain a viscosity increasing agent.

Similarly, a polyethylene oxide may be exemplified as the viscosityincreasing agent.

Similarly, the thermosetting resin composition which forms thethermosetting resin composition film which is hardened at roomtemperature may contain a polymerization retardant or inhibitor.

4-methoxyphenol may be exemplified as the polymerization retardantinhibitor.

Similarly, a molding tool in which the interior can be depressurized isemployable as the molding tool.

Similarly, the hardening of the thermosetting resin composition filmwhich is hardened at room temperature may be performed under adepressurized state.

Similarly, pressing an upper molding tool and/or a lower molding toolmay be included between; laminating a reinforced fiber material which issubstantially fee from a matrix resin; a glycol modifiedcopolymerization polyester resin film; a thermosetting resin compositionfilm which is hardened at room temperature; a core material selectedfrom an open cell foam and a honeycomb; a thermosetting resincomposition film which is hardened at room temperature; a glycolmodified copolymerization polyester resin film; and a reinforced fibermaterial which is substantially free from a matrix resin, in this orderin a molding tool to form a sandwich; and hardening the thermosettingresin composition film which is hardened at room temperature under theconditions that the molding tool is closed.

Similarly, a vinyl ester resin and an epoxy resin may be exemplified asthe matrix resin.

Similarly, a frame member which prevents the matrix resin frompenetrating into the core material may be disposed at the circumferenceof the core material.

The adhesive film of the present invention includes a glycol modifiedcopolymerization polyester resin film, and a thermosetting resincomposition which is hardened at room temperature, which is helduniformly on the glycol modified copolymerized polyester resin film.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, a preferred embodiment of the present invention will beexplained.

“Sandwich Structure”

The sandwich structure of the present invention is constituted from aresin board which is reinforced by a reinforcing fiber material as afacing material, and a core material which is put between the resinboards. As for the core material and the facing material of the sandwichstructure of the present invention, there are no particular limitationsin the thickness of the core material and the facing material, and hencethe thickness thereof can be designed corresponding to demandedcharacteristics.

“Molding Tool”

There are no particular limitations about the quality of the material ofthe molding tool in the present invention. The molding tool consists ofa single mold or double molds. In the case in which a single mold isemployed, when the single mold is used as a lower mold, a coveringmaterial such as a resin film is used as an upper mold. In this case,the mold may be used as the upper mold or the lower mold. It ispreferred that the interior of the molding tool of the present inventioncan depressurized.

“Reinforcing Fiber Material”

The reinforcing fiber material used in the present invention is notparticularly limited. For example, organic fibers such as a carbonfiber, a boron fiber, an aramid fiber, a polyethylene fiber, a liquidcrystal polymer fiber, and a polyacetal fiber; inorganic fibers such asa glass fiber, an alumina fiber and a silicon carbide fiber; and a metalfiber, etc., may be exemplified. In addition, these reinforcing fibertextiles and knittings in which the fibers were composited may also beused.

“Impermeable Resin Film”

The impermeable resin film of the present invention blocks the matrixresin which has not yet hardened thereby adhering to the matrix resinafter being hardened. For example, a modified polyester resin and apolyetherimide resin film may be exemplified. The impermeable resin ispreferably a glycol modified copolymerized polyester resin, and morepreferably a cycloalkanediol modified copolymerized polyester.

“The Thermosetting Resin Composition Film which is Hardened at RoomTemperature”

The thermosetting resin composition film which is hardened at roomtemperature used in the present invention is not necessarily solidindividually, and it may be one which consists of a liquid or a viscosethermosetting resin composition and a carrier which holds thethermosetting resin composition thereon. A resin film, a cloth-likematerial, a textile, a nonwoven fabric, or the like, may be exemplified,as the carrier.

They may preferably be a nonwoven fabric and a resin film. As for thethermosetting resin composition which is hardened at room temperaturewhich constitutes the thermosetting resin composition film which ishardened at room temperature, it is preferred to have a viscosity of 2to 200 Pa·s.

Here, if the viscosity is less than 2 Pa·s, the resin composition on theupper side of the core material falls below too much by gravity, and aproblem that a quantity required for adhering the facing material to thecore material cannot be held will arise. On the other hand, if theviscosity exceeds 200 Pa·s, a problem that the resin composition on theupper side of the core material hardly hangs down below by gravity, andcannot supply a quantity required for adhering the facing material tothe core material will arise.

A thermosetting resin having the viscosity can be selected and it canalso attain the viscosity by adding a thickening agent to athermosetting resin. By adjusting reaction time, it can also attain theviscosity by proceeding the reaction to increase the viscosity, therebylaminating it to the core material with a desired viscosity. Althoughthe thickening agent is not particularly limited, for example, apolycarbonate, a polystyrene, and a polyethylene oxide are preferred,and further, a polyethylene oxide is more preferred as the thickeningagent. As for the thermosetting resin composition which is hardened atroom temperature which constitutes the thermosetting resin compositionfilm which is hardened at a temperature, an epoxy resin, a vinyl esterresin, a polyester resin, a phenol resin, a urea resin, a melamineresin, a polyurethane resin, a polyimide resin, a PITI resin, a cyanateresin, a bismaleimide resin, a BCB resin, a COPNA resin, a gum resin, apoly benzimidazole resin, an acrylic resin, a cyanoacrylate resin, anacetic acid ester resin, a silicone resin, etc., may be exemplified, forexample. Preferably, the thermosetting resin composition which ishardened at room temperature which constitutes the thermosetting resincomposition film which is hardened at a temperature is constituted fromvinyl polymerizable compounds. A vinyl ester resin is more preferred. Tothe thermosetting resin composition which is hardened at roomtemperature which constitutes the thermosetting resin composition filmwhich is hardened at a temperature, a polymerization retardant can beadded, in order to extend the working life. For example, a 4-methoxyphenol, a hydroquinone, and a 2,4-pentadione may be exemplified. Apreferred polymerization retardant is 4-methoxy phenol.

“Core Material”

The core material used in the present invention is a hollow corematerial. Specifically, an open cell foam and a honeycomb material maybe exemplified. The open cell foam which is used in the presentinvention is not particularly limited. Either an open cell foam made ofan organic material and an open cell foam made of an inorganic materialmay be used. A polyurethane foam, a poly methacrylic imide foam, a polyacrylate foam, a polyvinyl chloride foam, a carbon foam, etc., may beexemplified.

The honeycomb material which is used in the present invention is notparticularly limited. Airy of a honeycomb material made of an organicmaterial, a honeycomb material made of a metallic material, and ahoneycomb made of an inorganic material may be used. An aluminumhoneycomb, a stainless steel honeycomb, a steel honeycomb, a Kevlar™honeycomb, a Nomex™ honeycomb, a carbon honeycomb, a polyvinyl chloridehoneycomb, a polypropylene honeycomb, a polyethylene honeycomb, apolyurethane honeycomb, a polycarbonate honeycomb, a poly ether imidehoneycomb, a ceramic honeycomb, etc., may be exemplified. An aluminumhoneycomb, a Nomex™ honeycomb, a Kevlar™ honeycomb, and a carbonhoneycomb are preferred.

“The Lamination Method of the Material”

In one piece of a molding tool, a desired amount of reinforcing fiberswhich have not yet substantially contained a matrix resin are arranged.Subsequently, an impermeable resin film and a thermosetting resin filmwhich is hardened at room temperature are arranged. Subsequently, afterdisposing a desired core material, the thermosetting resin film which ishardened at room temperature, the impermeable resin film, and a desiredamount of the reinforcing fibers which have not substantially containeda matrix resin yet are arranged respectively. Next, mold closing isperformed by joining another piece of the molding tool thereto or usinga bagging film such as a nylon film, etc. In the case in which themolding tool is both mold type, clamping pressure is applied thereto. Atthis time, the inside of the molding tool may be depressurized. In thecase in which the molding tool is a single mold type, the inside of thebag may be depressurized using a vacuum pump, etc. It is preferred thatthe thermosetting resin be hardened at the time of clamping the moldingtool in the case in which a two moldings type molding tool is used, orat the time of depressurized in the case in which a single molding typemolding tool is used, respectively, that is when the material in themolding tool is deformed along the inner wall of the molding tool.

“The Infusion Method of a Matrix Resin”

A matrix resin may be infused into the molding tool using positivepressure and may be sucked into the molding tool using negative pressurein the molding tool.

“The Hardening Method of the Matrix Resin”

The matrix resin can be hardened by a desired method. The matrix resinmay be hardened at room temperature, and may be heated to a desiredtemperature. When the inside of the molding tool is being depressurized,it is preferred to keep on depressurizing during hardening of the matrixresin.

WORKING EXAMPLES

Working Examples will be explained hereinafter; however, the presentinvention is not limited thereto,

Raw Materials Used

As carbon fiber textiles, TR3110MS (brand name, which is a product ofMitsubishi Rayon Co., Ltd.) was used.

As nonwoven fabric, the following ones were used. ECULE(TM) 3501A (aproduct of TOYOBOU Co., Ltd.) 3151A (a product of TOYOBOU Co., Ltd.)As thermoplastic film, DIAFIX PG-WHI (a product of Mitsubishi PlasticsInc.: 0.2 mm in thickness, 0.1 mm in thickness, and 0.05 mm inthickness) which was PET-G was used.As a thermosetting resin, the following ones were used.Vinyl ester resin: DERAKANE MOMENTUM 411-350 (a product of Dow ChemicalCo., Ltd.)Initiator: Trigonox 239A (a product of Akzo novel Co., Ltd.)Catalyst: NUODEX (a product of CONDEA Servo LLC; 6 wt % Cobalt ionsolution)Poly(ethylene oxide) (a product of Scientific Polymer Products, Inc. Mw400,000) was used as a thickening agent.

Moreover, 4-Methoxyphenol (product made from Sigma-Aldrich Co., Ltd.,99%) was used as a polymerization retardant.

The following were used as a honeycomb core.

Aluminum honeycomb: DURA 5056 1.6-3/8 (produced by Alcore, Inc.) (whichhas a thickness of 10 mm, a density of 26 kg/m³, and a cell size of 9.5mm)

Aluminum honeycomb: DURA 5056 3.4-1/4 (produced by Alcore, Inc.) (whichhas a thickness of 10 mm, a density of 55 kg/m³, and a cell size of 6.4mm)

Hereafter, a measuring method will be explained.

Flatwise Tensile Strength

Measurements were made according to ASTM C297. The sandwich panel wascut to 76 mm in length and 76 mm in width by a grinder cutter. Thesurface thereof was roughened by a sand blaster and fixed to an aluminumblock with an adhesive (Loctite Hysol EA 9309.3NA; having a cure time ofnot less than 48 hours at room temperature). The peel strength of thefacing material from the core was measured in the tensile test. Thenumber of measurements was set to 5.

The following were used as measuring apparatus.

Itron 4484

Load ell: 30 kN

Moreover, the crosshead speed was 0.5 mm/min.

Areal Weight

As to the areal weight, the sandwich panel was cut to 76 mm in lengthand 76 mm in width, by a grinder cutter. Using a slide caliper havingthe minimum scale of 0.01 mm, the length of the cut sandwich panel wasmeasured at three points in length and breadth, respectively to beaveraged. Area was calculated from this value. Weight was measured by anelectronic balance (the minimum of 0.1 mg). The value which is obtainedby dividing the weight of the panel sample by the area is set to theAreal weight. The unit thereof is g/m².

Working Example 1

A PET-G film (0.2 mm in thickness) (300 mm×210 mm) was disposed to atable, and a piece of nonwoven fabric ECULE 3501A™ (292 mm×203 mm) wasinstalled thereon. 34 g of a compounded vinyl ester resin forimpregnation (which was prepared by mixing a vinyl ester resin in anamount of 100 weight part, an initiator in an amount of 2 weight part,and a catalyst in an amount of 0.033 weight part, and then beingdegassed for 3 minutes under a negative pressure of not lessthan 0.085MPa) was impregnated quickly into the nonwoven fabric ECULE 3501A™ usinga putty knife to obtain an adhesion film (1). The areal weight ofimpregnated resin at this time was 5.7×10² g/m². One more adhesion film(1) was obtained similarly. A mold releasing agent was applied onto theother table, and dried. Subsequently, a piece of a thick nonwoven fabric(368 mm×279 mm) was disposed thereon, and one piece of peel ply (368mm×305 mm) and two pieces of carbon fiber textiles (318 mm×229 mm) weredisposed thereon. One piece of the adhesion film (1) was disposed ontothe disposed carbon fiber textiles, such that the nonwoven fabric mightcome upside the carbon fiber textiles. Subsequently, a honeycomb coreDURA 5056 1.6-3/8 ™(267 mm×178 mm) was disposed thereon, and theadhesion film (1) was disposed thereon such that the nonwoven fabricmight descend. And two pieces of carbon fiber textiles (318 mm×229 mm)were disposed thereon. Subsequently, one piece of peel ply (368 mm×305mm) was disposed thereon, and one piece of a thick nonwoven fabric (267mm×229 mm) was disposed firer thereon. An inlet for a liquid resin wasdisposed linearly and aside the core material for a sandwich structurematerial, such that the inlet should be parallel to the longitudinaldirection of the core material, and that the infused liquid resin canpermeate into both the nonwoven fablic on upper side and on lower side.Similar to the inlet, a deaerating port was disposed linearly at theopposite side of the inlet across the core material. Subsequently, a bagfilm made of nylon was made to cover it, and the bag film was sealedwith a sealing tape on the table. Subsequently, the inside of the bagwas deaerated to be not less than 0.085 MPa of negative pressure with avacuum pump. Bagging end time was 32 minutes after the timing when thecompounding of the vinyl ester resin for impregnating was completed. Thethermosetting resin for impregnating was made to impregnate into a 30mm×30 mm nonwoven fabric of ECULE™ to be allowed to stand on a nylonfilm, and hardening state of the vinyl ester resin for impregnating wasobserved. It was 233 minutes after the timing when the compounding ofthe vinyl ester resin for impregnating was completed, that the tackinessof the vinyl ester resin for impregnating was lost. After 390 minutesfrom the completion of compounding the vinyl ester resin forimpregnating a sufficient amount of the compounded vinyl ester resin(which was obtained by degassing a mixture of a vinyl ester resin in anamount of 100 weight part, an initiator in an amount of 2 weight par,and a catalyst in an amount of 0.1 weight par; for 3 minutes under anegative pressure of not less than 0.085 MPa) was sucked from the inletside using a negative pressure. The inlet was closed after being checkedvisually that the liquid resin had fully filled the inside of the bag.It was allowed to stand for a night while deaerating to harden thecompounded resin at a normal temperature, thereby obtaining a sandwichpanel (1) which was a sandwich structure. During the molding, thetemperature of the room was kept at 19° C.

Working Example 2

A sandwich panel (2) was obtained by performing the same process as inWorking Example 1, with the exception of adjusting the bagging end timeto be 56 minutes after the completion of compounding of the vinyl esterresin for impregnating, and of adjusting the time for infusing thematrix resin to be 277 minutes after the completion of compounding ofthe vinyl ester resin for impregnating. The temperature of the room waskept at 21° C. It was 125 minutes after the timing when the compoundingof the vinyl ester resin for impregnating was completed, that thetackiness of the vinyl ester resin for impregnating was lost.

Working Example 3

A sandwich panel (3) was obtained by performing the same process as inWorking Example 1, with the exception of adjusting the bagging end timeto be 45 minutes after the completion of compounding of the vinyl esterresin for impregnatinig, and of adjusting the time for injecting thematrix resin to be 284 minutes after the completion of compounding ofthe vinyl ester resin for impregnating. The temperature of the room waskept at 21° C. It was 121 minutes after the timing when the compoundingof the vinyl ester resin for impregnating was completed that thetackiness of the vinyl ester resin for impregnating was lost.

Working Example 4

A PET-G film (0.05 mm in thickness) (300 mm×210 mm) was disposed onto atable, and one piece of nonwoven fabric ECULE™ 3151A (292 mm×203 mm) wasdisposed thereon. 3.09 parts of a thickening agent (poly (ethyleneoxide)) and a 0.1 parts of a polymerization retardant (4-methoxyphenol)was added to a vinyl ester for impregnating (which is a mixture of avinyl ester resin in an amount of 100 parts by weight, an initiator inan amount of 4 parts by weight, and a catalyst in an amount of 0.033parts by weight), and agitated sufficiently. 23 g of a vinyl ester forimpregnating which was degassed for 3 minutes under a negative pressureof not less than 0.085 MPa was impregnated quickly to a nonwoven fabricECULE™ 3151A using a putty knife to obtain an adhesion film (2). Theareal weight of the impregnated resin at this time was 3.8×10² g/m². Onemore adhesion film (2) was obtained similarly. A mold releasing agentwas applied onto another table, and dried. Subsequently, one piece of athick nonwoven fabric (368 mm×279 mm) was disposed thereon, and onepiece of peel ply (368 mm×305 mm) and two pieces of carbon fibertextiles (318 mm×229 mm) were disposed thereon. One piece of theadhesion film (2) was disposed onto the disposed carbon fiber textiles,such that the nonwoven fabric might come above the carbon fibertextiles. Subsequently, a honeycomb core DURA 5056 1.6-3/8 (1 (267mm×178 mm) was disposed thereon, and the adhesion film (2) was disposedthereon such that the nonwoven fabric might come below. And two piecesof carbon fiber textiles (318 mm×229 mm) were disposed thereon.Subsequently, one piece of peel ply (368 mm×305 mm) was disposedthereon, and one piece of a thick nonwoven fabric (267 mm×229 mm) wasdisposed further thereon. An inlet for a liquid resin was disposedlinearly and aside the core material for a sandwich structure material,such that the inlet should be parallel to the longitudinal direction ofthe core material, and that the infused liquid resin can permeate intoboth the nonwoven fablic on the upper side and on the lower side.Similar to the inlet, a deaerating port was disposed linearly at theopposite side of the inlet across the core material. Subsequently, a bagfilm made of nylon was made to cover it, and the bag film was sealedwith a sealing tape on the table. Subsequently, the inside of the bagwas deaerated to be not less than 0.085 MPa of negative pressure with avacuum pump. Bagging end time was 65 minutes after the timing when thecompounding of the vinyl ester resin for impregnating was completed.After 2682 minutes from the completion of compounding the vinyl esterresin for impregnating, a sufficient amount of the compounded vinylester resin (which was obtained by degassing a mixture of a vinyl esterresin in an amount of 100 weight part, an initiator in an amount of 2weight part, and an accelerator in an amount of 0.1 weight part, for 3minutes under a negative pressure of not less than 0.085 MPa) was suckedfrom the inlet side using a negative pressure. The inlet was closedafter checked visually that the liquid resin had fully filled the insideof the bag. It was allowed to stand for a night while deaerating toharden the compounded resin at a normal temperature, thereby obtaining asandwich panel (4) which had a sandwich structure. During the molding,the temperature of the room was kept at 21° C.

Working Example 5

A sandwich panel (5) was obtained in the same way as in Working Example4, with the exception of substituting the honeycomb with DURA 50563.4-1/4, substituting the non-woven fabric with ECULE 3501A convertingthe thickness of the PET-G film into 0.1 mm, converting the impregnatingamount of the vinyl ester for impregnating into 33 g, adjusting thebagging end time to be after 52 minutes from the completion ofcompounding the vinyl ester resin for impregnating, and of adjusting thematrix resin injecting time to be after 3166 minutes from the completionof compounding the vinyl ester resin for impregnating. During themolding, the temperature of the room was held at 19° C.

Comparative Example 1

A mold releasing agent was applied onto a table and was dried.Subsequently, one piece of a thick nonwoven fabric (368 mm×279 mm) wasdisposed thereon, and one piece of peel ply (368 mm×305 nun) and twopieces of carbon fiber textiles (318 mm×229 mm) were disposed thereon.Subsequently, a honeycomb core DURA 5056 1.6-3/8™ (267 mm×178 mm) wasdisposed thereon, and two pieces of carbon fiber textiles (318 mm×229mm) were disposed thereon. Subsequently, one piece of peel ply (368mm×305 mm) was disposed thereon, and one piece of a thick nonwovenfabric (267 mm×229 mm) was disposed further thereon. An inlet for aliquid resin was disposed linearly and aside the core material for asandwich structure material, such that the inlet was parallel to thelongitudinal direction of the core material, and that the infused liquidresin can permeate into both the nonwoven fablic on the upper side andon the lower side. Similar to the inlet, a deaerating port was disposedlinearly at the opposite side of the inlet across the core material.Subsequently, a bag film made of nylon was made to cover it, and the bagfilm was sealed with a sealing tape on the table. Subsequently, theinside of the bag was deaerated to not less than 0.085 MPa of negativepressure with a vacuum pump. Thereafter, a sufficient amount of thecompounded vinyl ester resin (which was obtained by degassing a mixtureof a vinyl ester resin in an amount of 100 weight part, an initiator inan amount of 2 weight part, and an accelerator in an amount of 0.1weight part, for 3 minutes under a negative pressure of not less than0.085 MPa) was sucked from the inlet side using a negative pressure. Theinlet was closed after checking visually that the liquid resin had fullyfilled the inside of the bag. It was allowed to stand for a night whiledeaerating to harden the compounded resin at a normal temperature,thereby obtaining a sandwich panel (6) which was a sandwich structure.During the molding, the temperature of the room was held at 23° C.

Referential Example 1

A mold releasing agent was applied onto a table and was dried.Subsequently, two pieces of carbon fiber textiles (318 mm×229 mm) weredisposed thereon. One piece of peel ply (368 mm×305 mm) was disposedthereon, and one piece of a thick nonwoven fabric (295 mm×280 mm) wasdisposed thereon. The inlet for a liquid resin was formed linearly atthe center. Tow deaerating ports were formed at both sides of the carbonfiber textiles like 2, respectively, linearly similar to the inlet.Subsequently, a bag film made of nylon was made to cover it, and the batfilm was sealed with a sealing tape on the table. Subsequently, theinside of the bag was deaerated to be not less than 0.085 MPa ofnegative pressure with a vacuum pump. Thereafter, a sufficient amount ofthe compounded vinyl ester resin (which was obtained by degassing amixture of a vinyl ester resin in an amount of 100 weight part, aninitiator in an amount of 2 weight part, and an accelerator in an amountof 0.1 weight part, for 3 minutes under a negative pressure of not lessthan 0.085 MPa) was sucked from the inlet using a negative pressure. Theinlet was closed after being checked visually that the liquid resin hadfully filled the inside of the bag. It was allowed to stand for a nightwhile deaerating to harden the compounded resin at a normal temperature,thereby obtaining a carbon fiber composite sheet.

When an areal weight of the carbon fiber composite sheet was measure itwas 6.0×10² g/m². When an areal weight of nonwoven fabric ECULE™ 3501Awas measured, it was 48 g/m². When an areal weight of an aluminumhoneycomb DURA 5056 1.6-3/8 was measured, it was 2.7×10² g/m². When anareal weight of a PET-G film (0.2 mm in thickness) was measured, it was2.5×10² g/m².

To the sum of areal weights of two pieces of carbon fiber compositesheets, two pieces of a non woven fabric ECULE™, the aluminum honeycomb,and the two pieces of PET-G films, the areal weight of the impregnatingresin for two adhesion films were added, as a result, the total thereofbecame 3.2×10³ g/m².

Measurement

Test pieces were cut from the sandwich panel, and flatwise tensilestrength and areal weight thereof were measured. The results are shownin Table 1. TABLE 1 Sandwich panel 1 2 3 4 5 6 Flatwise tension strength1.7 1.1 2.1 2.6 3.4 — (MPa) Areal weight (g/m³) 3.2 × 10³ 3.2 × 10³ 3.2× 10³ 2.6 × 10³ 3.3 × 10³ 1.1 × 10⁴

In Comparative Example 1 which is a conventional method, the matrixresin permeated into the honeycomb cell, and hence the areal weight ofthe resultant panel produced therefrom is enormous. As shown in theReference Example, the calculated sum of the areal weight of each memberof the sandwich panel (1), (2), and (3) is 3.2×10³ g/m², and is the sameas the actual value of the areal weight of each sandwich panel ofWorking Examples. Therefore, it turns out that the permeation of thematrix resin into the core can be prevented by 100%. Moreover, as thepanel (4) indicated, reduction of sandwich panel weight and improvementin the peel strength of a facing sheet can be attained by optimizing themember and the additive amount of the resin for adhesion film, andadding of the thickening agent. Moreover, as the sandwich panel (5)indicated, peel strength can be increased by enlarging the cell size ofa honeycomb core.

In the present invention, it is possible to prevent the matrix resinfrom permeating into the core, and to adhere the impermeable resin filmof the present invention to the facing sheet, without heating forsealing the core. Moreover, the heating process can be completelyeliminated by using a matrix resin which can be hardened at roomtemperature. Therefore, according to the present invention, it ispossible to produce a sandwich structure without performing a headingoperation, when producing a sandwich structure including an unsealedhollow core, thereby reducing energy to be used and equipment cost.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A process for producing a sandwich structure comprising: laminating areinforced fiber material which is substantially free from a matrixresin; a glycol modified copolymerized polyester resin film; athermosetting resin composition film which is hardened at roomtemperature; a core material selected from an open cell foam and ahoneycomb; a thermosetting resin composition film which is hardened atroom temperature; a glycol modified copolymerized polyester resin film;and a reinforced fiber material which is substantially free from amatrix resin, in this order in a molding tool to form a sandwich,hardening the thermosetting resin composition film which is hardened atroom temperature under a condition that the molding tool is closed,infusing a matrix resin into the molding tool, and adjusting atemperature in the molding tool at room temperature or a hardeningtemperature of the matrix resin to harden the matrix resin.
 2. A processfor producing a sandwich structure as set forth in claim 1, wherein theglycol modified copolymerized polyester resin is a cycloalkanediolmodified copolymerized polyester resin.
 3. A process for producing asandwich structure as set forth in claim 1, wherein the glycol modifiedcopolymerized polyester resin is a cycloalkanediol modifiedcopolymerized polyethylene terephthalate resin.
 4. A process forproducing a sandwich structure as set forth in claim 1, wherein theglycol modified copolymerized polyester resin film and the thermosettingresin composition film which is hardened at room temperature previouslyform an adhesive film consisting of the glycol modified copolymerizedpolyester resin film and a thermosetting resin composition which ishardened at room temperature, which is held uniformly thereon.
 5. Aprocess for producing a sandwich structure as set forth in claim 1,wherein the thermosetting resin composition film which is hardened atroom temperature has a cloth as a carrier.
 6. A process for producing asandwich structure as set forth in claim 5, wherein the cloth used asthe carrier is a nonwoven fabric.
 7. A process for producing a sandwichstructure as set forth in claim 1, wherein the thermosetting resincomposition which forms the thermosetting resin composition film whichis hardened at room temperature has a viscosity of 2 to 200 Pa·S.
 8. Aprocess for producing a sandwich structure as set forth in claim 1,wherein the thermosetting resin composition which forms thethermosetting resin composition film which is hardened at roomtemperature consists of a vinyl polymerizable compound.
 9. A process forproducing a sandwich structure as set forth in claim 8, wherein thevinyl polymerizable compound is a vinyl ester resin.
 10. A process forproducing a sandwich structure as set forth in claim 8, wherein thethermosetting resin composition which forms the thermosetting resincomposition film which is hardened at room temperature contains aviscosity increasing agent.
 11. A process for producing a sandwichstructure as set forth in claim 10, wherein the viscosity increasingagent is polyethylene oxide.
 12. A process for producing a sandwichstructure as set forth in claim 8, wherein the thermosetting resincomposition which forms the thermosetting resin composition film whichis hardened at room temperature contains a polymerization retardant orinhibitor.
 13. A process for producing a sandwich structure as set forthin claim 12, wherein the polymerization retardant or inhibitor is4-methoxyphenol.
 14. A process for producing a sandwich structure as setforth in claim 1, wherein the molding tool is a molding tool which candepressurize the interior thereof.
 15. A process for producing asandwich structure as set forth in claim 1, wherein the hardening thethermosetting resin composition film which is hardened at roomtemperature is performed under a depressurized state.
 16. A process forproducing a sandwich structure as set forth in claim 1, furthercomprising pressing an upper molding tool and/or a lower molding toolbetween laminating a reinforced fiber material which is substantiallyfree from a matrix resin; a glycol modified copolymerization polyesterresin film; a thermosetting resin composition film which is hardened atroom temperature; a core material selected from an open cell foam and ahoneycomb; a thermosetting resin composition film which is hardened atroom temperature; a glycol modified copolymerization polyester resinfilm; and a reinforced fiber material which is substantially free from amatrix resin, in this order in a molding tool to form a sandwich, andhardening the thermosetting resin composition film which is hardened atroom temperature under a condition that the molding tool is closed. 17.A process for producing a sandwich structure as set forth in claim 1,wherein the matrix resin is a vinyl ester resin.
 18. A process forproducing a sandwich structure as set forth in claim 1, wherein thematrix resin is an epoxy resin.
 19. A process for producing a sandwichstructure as set forth in claim 1, wherein a frame member which preventsthe matrix resin from penetrating into the core material is disposed atthe circumference of the core material.
 20. An adhesive film, comprisinga glycol modified copolymerized polyester resin film, and athermosetting resin composition which is hardened at room temperature,which is held uniformly on the glycol modified copolymerized polyesterresin film.